A conventional capacitance-to-digital technique is used for sensing capacitance of a capacitor, and uses a limited number of digital codes to represent the different capacitances sensed thereby. Accordingly, it is unable to achieve a high sensing resolution and a wide sensible capacitance range at the same time. FIG. 1 shows a relationship between the sensible capacitance ranges and the sensing resolutions of a conventional capacitance-to-digital converter that has multiple sensible capacitance ranges with different sensing resolutions. Assuming that the conventional capacitance-to-digital converter of FIG. 1 uses one hundred digital codes to represent the capacitances sensed thereby, the sensing resolution is inversely proportional to capacitance variation per unit increment of the digital code (i.e., a greater capacitance variation per change of the digital code indicating a lower sensing resolution). Accordingly, in FIG. 1, a unit increment of the digital code represents capacitance variation of 0.14 pF in a sensible capacitance range of 2 pF-16 pF, a unit increment of the digital code represents capacitance variation of 0.48 pF in a sensible capacitance range of 16 pF-64 pF, and a unit increment of the digital code represents capacitance variation of 1.92 pF in a sensible capacitance range of 64 pF-256 pF. Thus, such a conventional capacitance-to-digital converter is unable to achieve a high resolution when sensing a larger capacitor.